The present invention relates to an external storage device to be attached to a host and, more particularly, to an optical disk device having a rack for receiving cartridges each accommodating an optical disk medium therein and a drive unit for recording and reproducing data from the disk medium.
Generally, an optical disk device includes a rack capable of accommodating a plurality of cartridges in a flat position one above another while spacing them apart by a predetermined distance. A drive unit is disposed below the rack for recording or reproducing data in or from the optical disk medium accommodated in the cartridge, as desired. A transport mechanism adjoins the rack and drive unit to convey the cartridge horizontally between the rack and the drive unit, turns over the cartridge, and transports the cartridge upward or downward. The rack, drive unit and transport mechanism are disposed in a rectangular housing. A designated one of the cartridges is conveyed from the rack to the drive unit by the transport mechanism while being turned over, if necessary. As the drive unit completes a recording or reproducing operation with the cartridge, the cartridge is again transported from the drive device to the rack by the transport mechanism.
It is a common practice with the above-described type of optical disk device to provide only one rack and only one or two drive units in the housing. This brings about a problem that the number of cartridges to be stored and the recording and reproducing ability cannot be increased without resorting to extra disk devices. This is also true even when the desired increase in the number of cartridges to be stored or in the recording and reproducing ability is small. As a result, the conventional device lacks efficiency in respect of cost, performance and space requirement.